This invention relates to the flocculation and conditioning of the flocculent in liquids prior to separation of solids from the liquids by gravity. It is primarily applicable to the removal of settlable impurities from liquids whereby suitable chemical coagulants are added to the liquid throughout to produce an insoluble flocculent which captures the impurities in the liquid. These impurities are subsequently removed by sedimentation. The condition of the flocculent during its growth is probably the most vital function in the liquid/solid separation stage. In order to provide for maximum efficiency, the chemicals are introduced into the liquid or water to be clarified in an initial mixing in which the liquid is subject to very rapid mixing so as to obtain a maximum dispersion of the added chemicals. This initial mixing may be effected in one or more stages depending on whether one or more chemicals are to be dispersed and whether there is any advantage in adding them to the liquid in sequence. As soon as the initial mixing of the chemicals with the liquid to be treated has been effected the conditioning of the liquid by intimate mixing of the flocculent formed in the liquid with the impurities therein commences. During initial stages of flocculation the treated liquid should ideally be subjected to an initial vigorous or intense conditioning action the intensity of which progressively diminishes as flocculation increases and the flocculent becomes more fragile and more easily broken up by too an intense a conditioning action. Ideally therefore as mentioned the conditioning action commences vigorously and progressively diminishes until the conditioning action is completed and the fully conditioned and flocculated liquid is ready for the sedimentation stage in which the solids are separated from the liquid by gravity.
The purpose of the conditioning therefore is to nurture the growth of the flocculent and repeatedly bring this into contact with the impurities in the liquid so that the impurities are enmeshed by the flocculent to the extent that at the completion of the flocculation virtually all impurities are trapped in the flocculent which is then suspended in a clarified liquid. If the correct chemical coagulants have been administered and the conditioning system has been efficient the flocculent will then rapidly settle in a well designed settling stage leaving a clarified liquid for surface withdrawal.